1. Technical Field
The present invention relates generally to an apparatus and method for skipping fractional motion estimation (FME) in high efficiency video coding (HEVC) and, more particularly, to an apparatus and method for skipping FME in HEVC using the sum of absolute differences (SAD) on a coding tree block (CTB) basis.
2. Description of the Related Art
HEVC (high efficiency video coding), which is a next-generation multimedia moving image compression standard, exhibits a compression ratio twice as high as existing H.264/AVC in terms of subjective picture quality and a compression ratio 1.5 times as high as existing H.264/AVC in terms of objective picture quality.
In general, HEVC is problematic in that the computational load of FME increases upon encoding because more various block sizes are used than in existing H.264/AVC, which directly leads to an increase in encoding rate and an increase in the hardware area of an encoder when a System On a Chip (SoC) is implemented.
In the HEVC standard, an increase in the encoding rate attributable to a reduction in the computational load of FME and a reduction in the hardware area of the encoder when implementing an SoC have become important factors.
U.S. Patent Application Publication No. 2003-0112872 discloses a method of performing mixed motion evaluation based on hierarchical search, in which a current SAD value is compared with a maximum SAD value and integer motion estimation (IME) is skipped if the current SAD value is smaller than the maximum SAD value.
Korean Patent Application Publication No. 2009-0079286 discloses a moving image motion estimation method and apparatus using a high-speed global search block matching algorithm, in which a partial SAD value is compared with a minimum SAD value and then IME is skipped.
Additionally, a thesis entitled “Fast Inter-Mode Selection in the H.264/AVC Standard Using a Hierarchical Decision Process” published on “TCSVT”, Vol. 18, No 2, Page 186 discloses a high-speed inter-mode selection method using hierarchical determination processing in the H.264/AVC standard, in which complexity is reduced in hierarchical stepwise processing.
However, the above conventional technologies disclose only a technology for omitting IME or reducing complexity in hierarchical stepwise processing, but do not disclose and suggest a technology for comparing a current SAD value with a previous SAD value on a CTB basis and skipping FME based on the results of the comparison. Furthermore, the conventional technologies are interested only in H.264/AVC, but do not mention an increase in the computational load of FME attributable to more various block sizes in HEVC.
In order to overcome an increase in the computational load of FME in the HEVC standard, when a calculated value using a current SAD value is larger than a calculated value using a previous SAD, a method of skipping FME and setting a weight applied to the previous SAD to a value lower than a weight applied to the current SAD is used because this case has a good possibility of redundant information in which FME results overlap IME results. This increases a probability of redundant information being eliminated compared to the case where the current SAD value is simply compared with the previous SAD value, thereby enabling more rapid HEVC to be achieved. Accordingly, there is an urgent need for this type of new FME skip technology in HEVC.